Expectations, eh? There's nothing to put a dent in your day like that horrible sinking feeling you get when, say, a blind date turns out to bear an irrepressible resemblance to the Wicked Witch of the West (or Shrek, if you want a male equivalent – never let it be said that we're not equal-opportunity analogy providers).

Ratchet & Clank: Size Matters bears some of the tell-tale signs of a game burdened by expectations. And joining Metal Gear Solid, Grand Theft Auto and Jak and Daxter as the latest PlayStation 2 super-smash series to make its way on to PSP, it's a pretty understandable situation. Just like the unsubtle moral embedded into countless American teenage movies, though, it's when the game takes a break from trying to impress that the true inner beauty shines through.

It certainly grabs your attention straightaway thanks to its trademarked Ratchet & Clank visuals, which shine on the PSP as a result of lovely animation, great cut-scenes and a near glitch-free frame rate. Most of your time is spent jumping around the many planets that the eponymous duo visit during their intergalactic journey, all the while smashing, shooting and generally laying the smack down upon the evil TechnoMite robots that get in the way.

Despite what the child-friendly characters and bright, varied environments may suggest, you see, Ratchet and Clank isn't really a platform game at all. Pixel-perfect jump demands are far outnumbered by the never-calming tidal waves of enemies washing against you while making progress.

Of course, tons of enemies requires tons of artillery, and the many weapons available to Ratchet – from energy guns to flamethrowers via shotguns and, um, mechanical bee-hives – are all so well balanced that it's difficult to choose between them. But choose you must, because each situation is best tackled with a strategy in mind.

Don't let appearances fool you: Size Matters can on occasion feel like a ruthless struggle, one which will often see you retrying the same section time after time, adjusting your plan with each new effort. Both Ratchet's life and his guns' effectiveness increase the more you battle, though, so these attempts never feel like wasted time, as each defeat makes you stronger – both literally and in terms of your ability as a player.

In addition to the large amount of shooting and adventuring on offer, there are also sections in which you control Clank, Ratchet's fun-sized robot companion. Thanks to an arsenal that encompasses his fists and, well, nothing else, Clank's sections are less about precise fighting and more about guiding Gadgebots, little robotic workers who can be commanded to attack enemies and perform tasks. These sections generally act as puzzles and serve as a welcome – if not particularly thrilling – break when all the gunplay gets a little too hectic.

In addition to this, the pair's adventure sees them faced with a wide array of diverse challenges, including countless hoverboard races and some destruction derby events for Crank to participate in. The best of the bunch, though, is the side-on Lemmings clone, in which Crank must give ever-moving Gadgebots orders to prevent them from falling to their doom.

Visually, Size Matters is striking, although the high-detail characters look out of place when framed within the comparatively basic environments. More impressive however are the high-quality cut-scenes that bookend levels, and which tell the occasionally amusing story very effectively thanks to snappy dialogue and accomplished voice acting.

It's not all good news: the lack of a second analogue stick and the occasionally slow auto lock-ons can cause the weapons to feel slightly clunky, possibly resulting in an over-reliance on Ratchet's melee attack. Similarly, strafing controls have had to be mapped to the D-pad, making it unnecessarily difficult to sidestep while maintaining target aim, something that the game often makes you feel you should be doing.

But possibly a greater concern is the lack of cohesion that the game suffers from. Sections such as the 'lock grinding' – where Ratchet shrinks himself down in order to unlock doors by grinding across inexplicably positioned rails – feel largely purposeless and tacked-on. Although none of the sections are bad, the constant switching from one style to another can prove jarring, and leads you to wonder whether all these distinct elements were really necessary.

Still, such moments are rare, and when all is said and done Size Matters remains one of the most enjoyable 3D action adventure experiences on the PSP. Boasting charming touches, rammed full of content and even trailing a Wi-Fi infrastructure multiplayer mode, it's an easy recommendation for anyone with an itchy trigger finger.

Expectations, eh? There's nothing like that feeling when something comes along that actually lives up to (most of) them.